Conventionally dump trucks are used for hauling earth, rock, rubble, asphalt and the like material but they have shortcomings, particularly when hauling extremely large loads, related to the necessity of elevating the box to empty its load. There is instability during elevation of the box due to side wind loads, soft and/or uneven ground, load freezing, wet material, sticking, flat or soft tires, worn fifth wheels, bushings, hinge pins and worn or broken springs. One or a combination of these factors can lead to sideways tipping of the trailer and the attached tractor or the truck on which it is mounted as the case may be, normally resulting in extensive damage. Another shortcoming is the inability to elevate the box due to overhead restrictions such as wires or structures. A further shortcoming is the lack of load control during dumping leading to an inability to spread material evenly as for example, when attempting to spread a cold asphalt mix or gravel on a road surface.
A principal object of the present invention is to provide a self-unloading unit, whether it be a truck or trailer type, built to overcome at least some of the foregoing problems through the use of an endless belt conveyor system on the floor in a non-elevating box with a level bottom floor.
It is known in the art to have endless bar type conveyors on the bottom floor of a cargo box to unload the contents in the box as exemplified by the teachings in U.S. Pat. No. 3,819,072 issued Jun. 25, 1974 to Edward A. Reed, U.S. Pat. No. 3,647,096 issued Mar. 7, 1972 to J.H. Holland and Canadian Pat. No. 1,204,084 issued May 6, 1986 to Krause Manufacturing, Inc. It is also known to use a belt which covers the floor and on which the contents rest as exemplified by the teachings of Canadian Pat. No. 895,158 issued Mar. 14, 1972 to Western Sawdust Products, Inc. It is also known to use friction reducing means under the belt for example, as disclosed in U.S. Pat. No. 3,481,647 issued Dec. 2, 1969 to L.A. Cook. While moving floor self unloading boxes are known, none are particularly suitable for bulk material haulage because of the absence of any provision to suitably loosen the material.